1. Technical Field
The present invention relates to rotor assemblies and liners within a gas turbine engine, and more particularly to radial clearance control between a rotor assembly and a liner disposed radially outside the rotor assembly.
2. Background Information
A gas turbine engine includes a fan section, a compressor section, a combustor section, and a turbine section disposed along a longitudinal axis. Air enters the engine through the fan section, passes through the compressor and into the combustor where fuel is mixed with the air and combusted. The combustion products, and any uncombusted air and/or fuel subsequently pass into the turbine and exit the engine through a nozzle. Collectively, the air and combustion products may be referred to as core gas, and the path through the fan, compressor, combustor, turbine, and nozzle referred to as the core gas path.
The fan, compressor and turbine sections include a plurality of rotor stages separated by stator sections. Each rotor stage includes a rotor assembly surrounded by a shroud. The rotor assembly includes a plurality of rotor blades attached to and circumferentially distributed around a disk. Radially outside of the rotor stage, the shroud defines the outer radial boundary of the gas path through that rotor stage. The outer radial surface of each rotor blade (i.e., the "blade tip") is positioned in close proximity to the inner radial surface of the shroud. The design clearance between the blade tips and the shroud is a predetermined value, chosen to minimize efficiency losses attributable to core gas passing between the blade tip and the shroud, while at the same time avoiding interference with the shroud. The actual clearance between the blade tips and the shroud will vary during operation of the engine.
What is needed is a method and an apparatus for controlling the actual clearance between a rotor stage and a shroud within a gas turbine engine, one that can predict instantaneous clearance values as a function of time, and one that can determine instantaneous clearance values under steady-state and transient conditions.